Thread: Stdin & fgets problem

Do not use magic numbers in your code.

fgets - C++ Reference
fgets info that makes your test different that real value.

A newline character makes fgets stop reading, but it is considered a valid character by the function and included in the string copied to str.

> using namespace std;
First off, this is C++ and not C.

Don't just type in random stuff and expect it to work.
That your visual studio defaults to C++ when you create a new project is a PITA when you're trying to write C.

> char c[70];
> char l[80];
> fgets(c, 100, stdin);
> while (fgets(l, 100, file)) {
DO NOT LIE about your buffer sizes.
There is no point protecting your toes with safety boots if you then go and lop off your entire leg with a chainsaw.

> fopen_s(&file, "some/path", "r")
vs
> errno_t err = fopen_s(&file, c, "r");
Because the buffer c will contain a \n from the fgets call you used to get input from the user.
You need to remove that newline.

You need to make better use of sizeof in order to avoid magic numbers, as was already mentioned, e.g.,

Code:

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    char filepath[80];
    if (!fgets(filepath, sizeof(filepath), stdin))
    {
        fprintf(stderr, "failed to read file path\n");
        return EXIT_FAILURE;
    }
    filepath[strcspn(filepath, "\n")] = '\0';

    FILE *file;
    errno_t err = fopen_s(&file, filepath, "r");
    printf("err:%d", err);
    char line[100];
    while (fgets(line, sizeof(line), file))
    {
        char *s1 = strstr(line, "VELOCITY");
        char *s2 = strstr(line, "POSITION");
        //doing somethings with s1 and s2
    }
    fclose(file);
 
    return 0;
}

You also need to make it such that you act on an error from fopen_s, not just print the error code then continue as if there's no error.

Notice that I named the variables with descriptive names.

Originally Posted by scorp08

I already said removed newline and got same error again, not understand why fail? Is ıt because sizeof(c) ? I only want top open a file from user input and readlines. So please write more understandable...

Saying you did something, and showing what you actually did are two completely different things.

Another common source of trouble is mistaking what the programs idea of 'current directory' is, which often varies depending on whether you run it from the IDE, double-click on it in explorer, or run it directly from the command line.

Show your work before complaining that something doesn't work.